The present invention relates to a method and apparatus for efficiently metering the flow of a fluid being removed from a container and, more particularly, to a method and apparatus for metering the flow rate by a weight of the fluid which is delivered per unit of time, in order to allow accurate measurement and control of the amount of fluid being removed.
Fluids which are delivered in bulk quantities for various applications typically utilize metering systems for measuring and controlling the amount of fluid delivered. An example of such an application is in the delivery of water treatment chemicals to cooling towers, boilers and other similar systems. Such an application would typically use a fluid delivery system such as a metering pump. While metering pumps can be set up to accurately dispense the chemicals, over time the pump may lose accuracy due to conditions such as, but not limited to, changes in inlet or discharge pressure, losing pump prime, outgassing from the fluid product, causing xe2x80x9cairlockxe2x80x9d, or damage to the supply or delivery lines. These conditions can result in a reduction of metering accuracy, or even stopping fluid delivery entirely.
In view of the foregoing, there is a need to verify that a fluid delivery system is functioning and how much fluid it has actually delivered. One existing system for metering fluid uses a volumetric method to measure fluid delivery. However, a volumetric system has disadvantages. For example, because fluid density and therefore volume are functions of temperature, equipment for measuring fluid in a volumetric system may need to be calibrated for temperature. Therefore, variations in temperature during product delivery over a period of time can introduce inaccuracies into measurement.
Accordingly, a metering system is needed which is easily repeatable and maintains accuracy over a range of temperatures.
A method and apparatus according to the present invention provides for improved accuracy of measurement of a rate of fluid delivery. A weight of a fluid being delivered is measured in timed cycles to provide for greater accuracy of measurement over a range of temperatures.
In a preferred embodiment, a metering device is connected between a fluid source and a fluid removal system such as a pump. The device includes an intermediary container having an inlet from the fluid source controlled by a valve. Weight-responsive means engaging the container control the valve to admit fluid into the container from the source. The weight-responsive means detect a change in the weight of the content of the container due to the fluid, and close the valve in response to the change in weight. The fluid removal system subsequently removes fluid from the container. The weight-responsive means detect a change in the weight of the container due to the removal of fluid, and subsequently re-open the valve to admit fluid. Repeating time periods between the closing and opening of the valve can thus be used for measurement of the fluid flow rate in terms of its weight.